Fixation and embedding variables in the immuno-electron microscopic study of rat Heymann nephritis

Fixation and embedding variables were compared in immuno-electron microscopic localization of rat IgG in an autologous immune complex-type nephritis. Specimens from kidney cortex were fixed for 3, 6 or 9 h in the following fixatives made in 0.1 M phosphate buffer at pH 7.4: 4% paraformaldehyde, 2.5% glutaraldehyde, periodate- lysine-paraformaldehyde or modified Karnovsky's fixative. Localization of IgG was performed on tissue sections cut with a tissue chopper, cryostat or sliding microtome, using agarose, Ames O.C.T. Compound or polyethylene glycol respectively as cutting matrixes. The sections were incubated in peroxidase-labelled antirat IgG antiserum (diluted 1:20 with phosphate-buffered saline) for 60 h. Peroxidase activity was then revealed and the sections embedded in Epon. Exact localization of IgG throughout the sections and good ultrastructure were achieved when paraformaldehyde and agarose were used. Periodatelysine-paraformaldehyde proved almost as useful as paraformaldehyde in connection with agarose in respect of peroxidase reaction and ultrastructure. Fixatives containing glutaraldehyde gave a mostly weak and unevenly distributed peroxidase reaction product. In the cryostat sections breaking of the tissue structure could not be avoided. When polyethylene glycol was used as cutting matrix no peroxidase reaction was achieved.